As is well known in the art, the slab type electrophoretic process (i.e., electrophoretic process for causing electrophoresis of a gel in the form of a vertical column) is superior in the operation control property, resolution, etc. to the disk type electrophoretic process, and is particularly superior in the separation of proteins, enzymes and peptites in large quantities. Further, it is sometimes suited for the separation of nucleic acid and physiologically active materials difficultly capable of heat treatment. Thus, it can find extensive applications in various researches and investigations in the biochemical fields. At present, it is generally used for the purity inspection of purified samples of proteins and nucleic acids and also as a most standard test method for the analysis of mixtures.
Thus, extensive researches and investigations have been conducted on electrophoretic media for analysis purposes in order to improve the separation performance or improve the gel strength to make gel more difficult to crumble.
As an example, Japanese Patent Disclosure No. 59543/89 discloses adding water-soluble polymers and denaturing materials to gels obtained through crosslinking polymerization of acrylamide type compounds to improve the brittleness and separability of the gels.
In case where proteins having catalytic activity such as enzymes is purified, a process in which the efficiency of recovery of the specific activity is high, i.e., the efficiency of recovery of intended enzymic protein is high, is more effective, and this is the most important consideration.
However, no research or investigation has been conducted on electrophoretic media with the purpose of separation.
As an example of the application of the principles underlying the electrophoresis to the separation and purification of particular materials, there is a gel holder disclosed in Japanese Patent Laid-Open No. 143651/92 (laid open on May 18, 1992).
Such gel holder used for the separation and purification of particular materials, is large in size because its purpose is the separation of proteins, enzymes, nucleic acids, etc. In addition, the amount of the electrophoretic medium used in one cycle for this end is 5 to 20 times the amount in the case of the usual electrophoresis. Therefore, it is sometimes required to have a strong performance of fulfilling the role of commonly termed "shieving", i.e., separating a sample according to the molecular size.
In another aspect, in a well-known process of recovering the enzymic protein after the electrophoresis, the electrophoretic medium in the intended enzyme part is cut out, and the cut-out medium is subjected to electric extraction by further electrolysis (Ziola. B.R. & Scraba. D.G. 1976, Anal. Biochem., 72, p-p 366-371). In another well-known process, the electrophoretic medium is physically crushed and suspended in a buffer solution for separation of the intended substance by centrifugal separation or filtering (Toshihisa Oshima & Hiroki Sakamoto, Biochem., 60. 5. p-p 374-377, 1988).
In the process using a gel holder for the electric extraction, the electrophoretic medium is cut in large quantities, thus dictating large size apparatus and long process time. In addition, it is liable that the enzyme or protein looses its activity. Therefore, this process is unsuitable. The physically crushing process requires no substantial time until completion of the crushing and recovery. However, it is thought that electrophoretic media are less peculiarly adsorptive with respect to enzymes, and there is a problem that the recovery of enzymic protein is greatly influenced by whether or not the crushing is made satisfactorily.
Therefore, the electrophoretic medium used for the gel holder is required to have the opposed properties that it has sufficient mechanical strength as material for separation at the time of the electrophoresis while being brittle and readily crumbled by physical crushing power at the time of the recovery of the enzymic protein. At present, there is no electrophoretic medium, which can sufficiently meet these two opposed requirements.
With a gel holder proposed by the applicant in an earlier application, the gel accommodated for separation in a gel accommodation section is engaged with projections formed therein. This structure thus is capable of preventing the falling of the gel to a certain extent, and it has been confirmed that purification can be obtained while maintaining the shape of the gel accommodated in the gel accommodation section to a certain extent even where the distance between gel clamping plates exceeds 1 cm, which has been a limit with the prior art mechanisms.
The applicant has conducted further researches and investigations with the earlier proposed gel holder noted above as a basis to reach a conclusion that for reliably preventing the gravitational fall of the gel and thus permitting the slab type electrophoretic analysis with higher accuracy, it is necessary to produce gel, which has a quite novel composition, as well as providing a gel holder suitable for such novel gel and a novel slab type electrophoretic apparatus using such novel gel and gel holder. Further, it is concluded that it is necessary to provide a gel cutter, which can readily cut large size gels extracted for the purpose of large quantity separation.